Purdue forage specialist: Evaluate alfalfa stands this fall

October 18, 2013

WEST LAFAYETTE, Ind. - Farmers should not ignore alfalfa fields after the final harvest of the season but instead should assess stands to determine if any limestone, nutrients or reseeding plans are necessary, a Purdue Extension forage specialist says.

Alfalfa is a high-quality forage well suited as a component of many rations for ruminant livestock and horses. The perennial plant requires a higher soil pH, ranging from 6.6 to 7.2, than most other forages and agronomic crops. Because changing soil pH can take time, Keith Johnson said producers should look at their alfalfa stands now to see if they are adequate or if new seeding should be planned in the spring of 2014.

"Producers should evaluate the density of the stand and determine if soil fertility, diseases, too frequent harvest or other stresses might be the reason for the decline," he said.

Over time, alfalfa plant density naturally lessens. Thickening a stand is difficult because alfalfa does not readily reseed itself, and over seeding is not successful because of competition with existing plants and autotoxicity - a process in which established alfalfa produces a chemical that can reduce establishment and growth of new plants.

According to Purdue University research, a satisfactory population is approximately 35 well-growing stems per square foot. Knowing the plant density gives producers a benchmark to measure how well their alfalfa is doing.

"If the stand is thin, it may be wise to consider establishing a new field in 2014," Johnson said.

When choosing a new field location, growers need to remember that alfalfa prefers a well-drained and deep soil. They also need to review labels of herbicides used in fields in 2013 for the plant-back restriction for alfalfa.

Something else Johnson said growers should consider is soil testing.

"If a soil test has not been taken in the past couple of years it would be advised to get one taken immediately," he said. "If soil pH is low, growers should follow through with limestone application yet this fall. Soil pH change is not immediate after limestone application, so getting it applied at least six months in advance of seeding is best."

Information about alfalfa production is available in Purdue Extension's Forage Field Guide. The guides can be purchased for $7 each from Purdue Extension's The Education Store by searching ID-317.